Polyethylene terephthalate blends

ABSTRACT

Thermoplastic compositions comprising, in intimate admixture, polyethylene terephthalate and a rubber-modified graft copolymer of a vinyl aromatic compound and an α,β-unsaturated cyclic anhydride. These compositions display desirable thermal properties, particularly elevated heat deflection temperatures.

REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of prior copending application Ser. No.162,138 filed June 23, 1980.

BACKGROUND

Polyethylene terephthalate (PET) has become an important raw materialfor production of moldings, film and fibers. Preparation of PET isdescribed inter alia in Whinfield et al., U.S. Pat. No. 2,465,319 and inPengilly, U.S. Pat. No. 3,047,539, and in Kirk-Othmer, Encyclopedia ofChemical Technology, Second Edition, Vol. 16, pp. 159 et seq. (1968),all disclosures being incorporated herein by reference.

Many applications for injection and extrusion molded parts require heatresistance, and it is in such applications that PET manifests certainundesirable properties. Unreinforced PET has been of limited interestfor making such parts due to its low HDT (Heat DeflectionTemperature)--about 75° C. at 264 psi. HDT is a measure of an importantthermal property of a thermoplastic material wherein a bar of thematerial, held in flexure under constant load (usually at 264 or 66psi), deforms a specified amount and the temperature at which thisspecified deformation occurs is the HDT--see Billmeyer, Textbook ofPolymer Science, p. 112, John Wiley and Sons, Inc. (1962).

U.S. Pat. No. 3,644,574 discloses blends of 1,4-butanediol polyesterswith from about 1 to about 40 weight percent of a vinyl aromatic polymer(e.g., a styrenic polymer) which polymer may be, inter alia, a copolymerwith maleic anhydride. The blends of this patent exhibit increased HDTover the unblended polyester. However, that patent discloses at Column1, lines 42-47 that the improvements observed with polybutyleneterephthalate are not obtained when the polyester is poly(ethyleneterephthalate).

SUMMARY OF THE INVENTION

The present invention provides a thermoplastic composition whichcomprises an intimate admixture of: (a) a polyethylene terephthalate and(b) a rubber-modified graft copolymer of a vinyl aromatic compound andan α,β-unsaturated cyclic anhydride.

The blends of this invention have a heat deflection temperature of atleast about 80° C., preferably above about 90° C., at 264 psi asmeasured by the ASTM procedure D 648-72. In a preferred embodiment, thecopolymer is a rubber-modified copolymer of a styrene, preferablystyrene, and maleic anhydride.

DETAILED DESCRIPTION OF THE INVENTION

The polyethylene terephthalate used herein is preferably homopolymericPET. Halogenated PET can also be used and is normally formed bycondensation of a mixture of a halogenated, preferably brominated,terephthalic acid (e.g., 2,5-dibromoterephthalic acid and2,3,5,6-tetrabromoterephthalic acid) and terephthalic acid with ethyleneglycol. Additionally, the polyethylene terephthalate used herein canalso contain up to 10 mol percent, relative to the acid component, ofradicals of other aromatic dicarboxylic acids such as, for example,phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid,diphenyl-4,4'-dicarboxylic acid and the like as well as theirhalogenated counterparts. The copolymers can also contain up to 10 molpercent, relative to the glycol component, of radicals of other glycolssuch as, for example, propylene glycol, butylene glycol,dibromoneopentyl glycol, bis(2-hydroxyethyl) ether oftetrabromobisphenol A and tetrabromo-p-xylylene glycol. See for exampleKirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, Vol.16, pp. 161-173 (1968).

The polyethylene terephthalates used herein should be moldable (i.e.,injection moldable or moldable by extrusion), and thus generally willhave an intrinsic viscosity (I. V.) falling between about 0.25 and 1.5,and more usually between about 0.5 and 1.2, as measured at 25° C. usinga solvent consisting of 60 percent by weight phenol and 40 percent byweight of tetrachloroethane. For best results the polyethyleneterephthalate should have an I. V. (measured in the foregoing manner) inthe range of 0.4 to 1.2, more preferably between 0.5 and 1.1, and formost injection molding applications polyethylene terephthalates in whichthe I. V. is in the range of 0.5 to 0.9 are deemed most desirable.

The amount of polyethylene terephthalate resin used in the blends ofthis invention preferably falls within the range of from about 10 toabout 90 weight percent based on the total weight of resin in the blendand the amount of the unsaturated cyclic anhydride copolymer fallswithin the range of from about 90 to about 10 weight percent also basedon the total weight of resin in the blend. In a particularly preferredembodiment the relative amounts of the PET and the copolymer fall withinthe range of from about 20 to about 80 and from about 80 to about 20weight percent, respectively, the total being equal to 100. Mostpreferably the amounts used fall within the range of 30 to 70 and fromabout 70 to 30 weight percent, respectively.

Copolymers of a vinyl aromatic compound and an α,β-unsaturated cyclicanhydride are well known in the art and are described in the literature.In general, they are prepared by conventional bulk or solutiontechniques using free-radical initiation. For example, styrene-maleicanhydride copolymers can be obtained by simply reacting the twomonomers, i.e., styrene and maleic anhydride, at 50° C. in the presenceof benzoyl peroxide. The rate of polymerization may be better controlledif a solvent such as acetone, benzene or xylene is used.

Vinyl aromatic compounds of component (b) can be derived from compoundsof the formula: ##STR1## where R¹ and R² are selected from the groupconsisting of (lower) alkyl groups of from 1 to 6 carbon atoms andhydrogen. R³ and R⁴ are selected from the group consisting of chloro,bromo, hydrogen and (lower) alkyl of from 1 to 6 carbon atoms; R⁵ and R⁶are selected from the group consisting of hydrogen and (lower) alkylgroups of from 1 to 6 carbon atoms or R⁵ and R⁶ may be concatenatedtogether with hydrocarbyl groups to form a naphthyl group. Thesecompounds are free of any substituent that has a tertiary carbon atom.Styrene is the preferred vinyl aromatic compound.

The cyclic anhydride compounds of component (b) are preferablyα,β-unsaturated dicarboxylic anhydrides. For example, the term cyclicanhydride identifies anhydrides having the formula: ##STR2## wherein thedotted lines represent a single or a double carbon-to-carbon bond, R⁷ isselected from the group consisting of hydrogen, alkyl or aryl radicalscontaining up to 8 carbon atoms, R⁸ is selected from the groupconsisting of hydrogen, vinyl, alkyl, alkenyl, alkylcarboxylic oralkenyl carboxylic of from 1 to 12 carbon atoms and n is an integer offrom 0 to about 10. Examples include maleic anhydride, methyl maleicanhydride, dimethyl maleic anhydride, citraconic anhydride, itaconicanhydride, phenylmaleic anhydride, aconitic anhydride, and mixturesthereof. Maleic anhydride is the preferred anhydride of component (b).

Copolymers of vinyl aromatic compounds and α,β-unsaturated cyclicanhydrides which can be used are described in U.S. Pat. Nos. 2,769,804;2,971,939 and 3,336,267.

In preparing the rubber-modified copolymers use of such rubbers aspolybutadiene, an isobutylene-isoprene copolymer, a styrene-butadienecopolymer, a butadiene-acrylonitrile copolymer, an ethylene-propylenecopolymer, a polyisoprene, ethylene-propylene-diene monomer terpolymers(EPDM) and the like can be employed. For a description of a typicalmethod of preparing the rubber-modified graft copolymers see U.S. Pat.No. 3,919,354 which is incorporated herein by reference.

Component (b) copolymers can comprise from about 40 to about 5 parts byweight of the α,β-unsaturated cyclic anhydride, from about 60 to about95 parts by weight of a vinyl aromatic compound, and up to 50 parts byweight of the rubber. Preferred polymers include those wherein therelative proportions of the styrene and the anhydride fall within therange of from about 90 to about 70 weight percent and from about 10 toabout 30 weight percent, respectively. Preferred rubber-modifiedpolymers used herein contain about 5-25 parts by weight of theα,β-unsaturated cyclic anhydride, 40-85 parts by weight of the vinylaromatic compound, and from about 5 parts to about 30 parts by weight ofrubber.

A preferred unmodified vinyl aromatic α,β-unsaturated cyclic anhydridecopolymer useful in the compositions of this invention is Dylark®332,supplied by ARCO/Polymers, Inc. Dylark®332 is a styrene-maleic anhydridecopolymer containing about 14 percent maleic anhydride, the balancebeing styrene. Still another preferred unmodified vinyl aromaticα,β-unsaturated cyclic anhydride copolymer is Dylark®DKB 134, also madeby ARCO/Polymers. This SMA copolymer contains about 17 percent maleicanhydride, the balance being styrene. A preferred rubber-modified vinylaromatic α,β-unsaturated cyclic anhydride copolymer is Dow ExperimentalResin XP-5272.07 made by Dow Chemical Company. This is a high impactstyrene-maleic anhydride copolymer believed to contain about 21.5 weightpercent butadiene, about 21 weight percent maleic anhydride and about57.5 weight percent styrene. Still another preferred rubber-modifiedcopolymer is Dylark®350 (ARCO/Polymers) containing 15 percent by weightrubber, 11 percent maleic anhydride, with the balance being styrene.Still other preferred rubber-modified copolymers are identified in theExamples hereinafter. Typically such preferred graft copolymers willcontain from 4 to 25 weight percent rubber, from 10 to 25 weight percentcyclic anhydride, and from 50 to 85 weight percent vinyl aromaticcompound.

Compositions of this invention can also include other ingredients, suchas flame retardants, extenders, processing aids, pigments, stabilizersand the like, for their conventionally employed purposes. Reinforcingfillers, in amounts sufficient to impart reinforcement, can be used,such as carbon filaments; silicates, e.g., acicular calcium silicate;asbestos; titanium dioxide; potassium titanate; titanate whiskers; andglass flakes and fibers.

Particularly preferred compositions of this invention include thosecontaining impact modifiers. Examples include ethylene/vinyl acetatecopolymers, ethylene/acrylic acid copolymers (having some of the acidfunctions neutralized), ethylene/methacrylic acid copolymers (havingsome of the methacrylic acid functions neutralized), ethylene/alkylacrylate/methacrylic acid terpolymer (also having some of themethacrylic acid functions neutralized), ABS, oxidized polyethylene,styrene-butadiene-styrene (S-B-S) block copolymers, styrene/butadienemultiblock copolymers, styrene/butadiene radial block copolymers,hydrogenated S-B-S block copolymers, styrene/butadiene rubber, acrylicrubbers, EPDM, ethylene/acrylic acid copolymers, ethylene/methylacrylate copolymers, ethylene/ethyl acrylate copolymers, polyester-ethermultiblock copolymers, and the like. These materials are available in awide range of molecular weights and it is generally desirable that theimpact modifier, when used, have a melt viscosity close to that of thesubstrate. Amounts of impact modifiers generally fall within the rangeof from about 5 to about 40 percent by weight. The results obtained inany given situation will, of course, depend upon a variety of factorssuch as the impact modifier selected, the manner by which it iscompounded into the blends, the concentration in which it is employed,and indeed upon the criteria used in measuring or judging the toughnessof the resultant blend. On the basis of the work performed thus far, themost preferred impact modifiers are the polyether-ester segmented blockcopolymers, a number of which are available commercially from du Pontunder the trademark Hytrel®. The composition and synthesis of thesecopolyetherester block copolymers have been described in theliterature--see for example U.S. Pat. Nos. 3,784,520; 3,766,146 and3,763,109, the disclosures of which are incorporated herein byreference. Note also the text of U.S. Pat. No. 4,259,458 from Column 13,line 15 through Column 17, line 23 which likewise is incorporated hereinby reference.

For protection against thermo-oxidative degradation, the customaryamounts of stabilizers, preferably 0.001 to 0.5 percent by weight,relative to the unfilled and unreinforced compositions of thisinvention, can be added to the compositions according to the invention.Examples of suitable stabilizers are phenols and phenol derivatives,preferably sterically hindered phenols which contain alkyl substituentswith 1-6 carbon atoms in the two positions ortho to the phenolichydroxyl groups, amines, preferably secondary arylamines and theirderivatives, phosphates and phosphites, preferably the aryl derivativesthereof and quinones. Non-limiting examples include4,4'-bis-(2,6-di-tert-butylphenol);1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)benzene;4,4'-butylidene-bis-(6-tert-butyl-m-cresol);3,5-di-tert-butyl-4-hydroxybenzyl-phosphonic acid diethyl ester;N,N'-bis(β-naphthyl)-p-phenylenediamine;N,N'-bis-(1-methyl-heptyl)-p-phenylenediamine; phenyl-β-naphthylamine;4,4'-bis(α,α-dimethylbenzyl)diphenylamine; hydroquinone; p-benzoquinone;toluhydroquinone; p-tert-butylpyrocatechol; chloranil; andnaphthoquinone.

Flame-retarding additives which can be used for the compositionsaccording to the invention comprise a large number of chemical compoundswhich are well known to those skilled in the art. In general, theycontain chemical elements which are used because of theirflame-retarding capacity, for example bromine, chlorine, antimony,phosphorus and nitrogen. Preferably, the flame-retarding additives arehalogenated organic compounds (brominated or chlorinated), optionallyused together with auxiliary compounds sometimes referred to assynergists, such as antimony trioxide, zinc borate, or the like.Elementary phosphorus or phosphorus compounds such as ammoniumpolyphosphate are also preferred flame retardants. Other examplesinclude bromine or chlorine containing organic phosphate esters,hexaphenoxyphosphazene, and the like.

Preferred reinforcing fillers are fiberglass, mineral fillers,particulate fillers such as mica and the like. In general, optimumphysical properties can be obtained if glass filaments are employed inamounts of from about 5 to about 40 percent by weight, based on thecombined weight of glass and resin. However, higher amounts can be used.

Compositions of the invention may be prepared by blending the componentsin a mixer (e.g., a Henschel mixer) and compounding the mixture on anextruder (e.g., a twin-screw compounding extruder such as a 28 mmWerner-Pfleiderer extruder or the like). Thereafter, the extrudate ischopped into pellets and molded on an injection molding machine.

The present invention is further illustrated in the following examples,which are not to be construed as limiting. All parts are by weight.

EXAMPLES I AND II

Compositions of the following examples were prepared by mixing thecomponents to form a premix, compounding the premix on a single screwextruder at temperatures about 525° to 550° F. (274°-288° C.), andmolding the pellets into test bars on a New Britain injection moldingmachine.

The particular materials used in these compositions were as follows:

a. Polyethylene terephthalate; from Goodyear Tire and Rubber Company;VFR 2977A-crystalline PET having an intrinsic viscosity of 0.68±0.025 asmeasured at 25° C. using a solvent consisting of 60 percent by weightphenol and 40 percent by weight of tetrachloroethane.

b. Styrene/maleic anhydride copolymer; from ARCO/Polymers; Dylark®DKB134.

The PET/SMA copolymer weight:weight ratio in the blend of Example I was70:30 and that of Example II was 60:40. Test bars of the abovecompositions were tested according to ASTM procedures to evaluatephysical properties. The ASTM designation numbers for the propertiesmeasured were as follows: Specific Gravity--D792-66 (1975);Tensile-Yield, Elongation and Tensile Elastic Modulus--D 638-77a;Flexural Strength and Flexural Elastic Modulus--D 790-71 (1978); IzodImpact for 1/4" bar, 1/8" bar and 1/8" bar at -40° C.--D 256-78; HeatDeflection Temperature--D 648-72 (1978); Vicat Softening Point--D1525-76; and Rockwell Hardness--D 785-65 (1976). The results are shownin Table I.

                  TABLE I                                                         ______________________________________                                        Property             Example I Example II                                     ______________________________________                                        Specific Gravity     1.260     1.247                                          Tensile-Yield, psi   7310      7590                                           Elongation, %        1.6       2.0                                            Tensile Elastic Modulus, 10.sup.3 psi                                                              470       447                                            Flexural Strength, psi                                                                             12,700    13,500                                         Flexural Elastic Modulus, 10.sup.3 psi                                                             441       465                                            Izod Impact, 1/4" bar, ft.-lb./in.                                                                 0.4       0.3                                            Izod Impact, 1/8" bar, ft.-lb./in.                                                                 0.4       0.3                                            Izod Impact, 1/8" bar, ft.-lb./in.                                            (at -40° C.)  0.4       0.3                                            Heat Deflection Temp. at 264 psi, °C.                                                       95        94                                             Heat Deflection Temp. at 66 psi, °C.                                                        120       117                                            Vicat Softening Point, °C.                                                                  207       195                                            Rockwell Hardness, R Scale                                                                         120       119                                            ______________________________________                                    

EXAMPLES III-XII

The following components were blended and molded as described inExamples I and II.

a. Polyethylene terephthalate--Cleartuf®8502A; from the Goodyear Tireand Rubber Company having an intrinsic viscosity of 0.85 as measured at25° C. using a solvent consisting of 60 percent by weight phenol and 40percent by weight of tetrachloroethane.

b. Styrene/maleic anhydride copolymer; Dylark®332 from ARCO/Polymers.

The proportions (weight percentages) used were as follows:

    ______________________________________                                                    Example                                                           Components    III      IV    V     VI  VII                                    ______________________________________                                        a.    PET         70       55  40    25  10                                   b.    Styrene/Maleic                                                                Anhydride   30       45  60    75  90                                   ______________________________________                                    

Physical property testing as in Examples I and II gave the results shownin Table II.

                  TABLE II                                                        ______________________________________                                                        Examples                                                      Property          III    IV     V    VI   VII                                 ______________________________________                                        Tensile Yield, 10.sup.3 psi                                                                     8.89   8.26   7.90 6.57 6.27                                Elongation, %     2.8    2.1    1.8  2.8  1.4                                 Tensile Modulus, 10.sup.3 psi                                                                   434    456    482  497  424                                 Flexural Strength, 10.sup.3 psi                                                                 15.2   13.3   13.1 11.6 10.4                                Flexural Modulus, 10.sup.3 psi                                                                  441    455    473  480  485                                 Notched Izod, 1/8" bar,                                                       ft.-lb./in.       0.3    0.3    0.2  0.2  0.2                                 Unnotched Izod, 1/8" bar,                                                     ft.-lb./in.       6.8    5.4    3.8  2.8  2.0                                 Heat Deflection Temp.                                                         at 264 psi, °C.                                                                          84     105    105  109  110                                 Heat Deflection Temp.                                                         at 66 psi, °C.                                                                           110    122    121  120  121                                 ______________________________________                                    

EXAMPLES VIII-XII

Rubber-modified styrene/maleic anhydride copolymers were blended andmolded in the same manner outlined in Examples I and II. The followingcomponents were used:

a. Polyethylene terephthalate-Vituf®5900; from Goodyear ChemicalCompany, having an intrinsic viscosity of 0.59 as measured at 25° C.using a solvent consisting of 60 percent by weight phenol and 40 percentby weight of tetrachloroethane.

b. Styrene/maleic anhydride copolymer; Dylark®332 from ARCO/Polymers.

c. Rubber-modified SMA containing 15 percent rubber, 11 percent maleicanhydride, with the balance being styrene; Dylark®350 fromARCO/Polymers.

d. Rubber-modified SMA believed to contain 21.5 weight percentbutadiene, 21 weight percent maleic anhydride and 57.5 weight percentstyrene; Dow XP 5272.07 from Dow Chemical Company.

The proportions (weight percentages) used were as follows:

    ______________________________________                                                   Examples                                                           Components   VIII    IX      X     XI    XII                                  ______________________________________                                        a.  PET          70      55    66.7  50    60                                 b.  Styrene/Maleic                                                                Anhydride    30      45    None  None  None                               c.  Rubber-Modified                                                               Styrene/Maleic                                                                Anhydride    None    None  33.3  50    None                               d.  Rubber-Modified                                                               Styrene/Maleic                                                                Anhydride    None    None  None  None  40                                 ______________________________________                                    

Physical property testing as in Examples I and II gave the results shownin Table III.

    ______________________________________                                                        Examples                                                      Property          VIII   IX     X    XI   XII                                 ______________________________________                                        Notched Izod, 1/8" bar,                                                       ft.-lb./in.       0.3    0.3    0.5  0.6  0.6                                 Unnotched Izod, 1/8" bar,                                                     ft.-lb./in.       6.9    4.8    16.0 11.5 20.8                                Heat Deflection Temp. at                                                      264 psi, °C.                                                                             87     95     87   96   85                                  Heat Deflection Temp. at                                                      66 psi, °C.                                                                              124    117    119  117  137                                 ______________________________________                                    

COMPARATIVE EXAMPLE

The PET used in Examples XIII-XII was molded in the manner outlined inExamples I and II. Physical property testing in accordance with the ASTMprocedures of Examples I and II showed the neat PET to have a HDT of 76°C. at 264 psi, a HDT of 104° C. at 66 psi, a 1/8 inch notched Izodimpact of 0.6 ft.-lb./in., a flexural strength of 15,200 psi and aflexural modulus of 400,000 psi.

EXAMPLES XIII-XV

Additional blends were made from the PET referred to in ExamplesVIII-XII using either Dylark®350 rubber-modified SMA or Dylark®338S, arubber-modified SMA containing about 4 weight percent rubber and 13.4weight percent maleic anhydride with the balance being styrene. Themakeup of the blends and their heat deflection temperatures at 264 psi(°C.) are shown in Table IV.

                  TABLE IV                                                        ______________________________________                                        Ex-               Wt. Percentage                                                                            Heat Deflection                                 ample Components  in Blend    Temperature of Blend                            ______________________________________                                        XIII  PET         50                                                                Dylark® 350                                                                           50           87                                             XIV   PET         55                                                                Dylark® 338S                                                                          45          104                                             XV    PET         50                                                                Dylark® 338S                                                                          50          100                                             ______________________________________                                    

EXAMPLES XVI-XIX

Four blends were made using an SMA graft copolymer composed of about 16weight percent maleic anhydride, 59 weight percent styrene and 25 weightpercent rubber. The same PET as in Examples VIII-XII was used. Table Vgives the heat deflection temperatures at 264 psi (°C.) of the blends.

                  TABLE V                                                         ______________________________________                                                   Wt. Percentage                                                                            Heat Deflection                                        Example    PET/SMA     Temperature of Blend                                   ______________________________________                                        XVI        85/15       78                                                     XVII       70/30       80                                                     XVII       55/45       87                                                     XIX        40/60       80                                                     ______________________________________                                    

EXAMPLES XX-XXVII

Eight blends were prepared using a PET from American Hoechst Companyidentified as Hoechst 018 and having an intrinsic viscosity (measured asabove) of 0.60. In each case a mixture of two different SMA copolymerswas used, one SMA being the rubber-modified graft copolymer referred toin Examples XVI-XIX, the other being either an unmodified copolymercontaining 18 weight percent maleic anhydride (DKB-290) fromARCO/Polymers, Inc.) or Dylark®338S rubber-modified SMA (note ExamplesXIV and XV above). Four of these blends were prepared by a double passextrusion-compounding procedure in which the two SMA copolymers wereblended together in the first-pass and the PET was added in thesecond-pass. Izod impact and heat deflection temperature (264 psi) dataare given in Table VI.

                                      TABLE VI                                    __________________________________________________________________________                  Example                                                                       XX XXI                                                                              XXII                                                                              XXIII                                                                             XXIV                                                                              XXV                                                                              XXVI                                                                              XXVII                                  __________________________________________________________________________    Blend Composition, wt %                                                       PET           70 70 55  55  55  55 40  40                                     SMA (Ex. XVI-XIX)                                                                           20 20 30  30  30  30 40  40                                     DKB-290       10 -- 15  15  --  -- 20  --                                     Dylark® 338S                                                                            -- 10 --  --  15  15 --  20                                     Melt Compounding Method                                                       Number of Passes                                                                            2  2  1   2   1   2  1   1                                      Properties                                                                    1/8" Notched Izod,                                                            ft.-lb./in.   0.6                                                                              0.8                                                                              0.7 0.8 0.7 1.1                                                                              0.6 0.7                                    1/8" Unnotched Izod,                                                          ft.-lb./in.   15.3                                                                             18.3                                                                             12.0                                                                              18.7                                                                              9.5 18.9                                                                             9.9 10.9                                   HDT at 264 psi, °C.                                                                  81 79 90  85  90  84 91  91                                     __________________________________________________________________________

EXAMPLES XXVIII-XXIX

A pair of blends of this invention were formed from the Hoechst 018 PETand Dylark®338S rubber-modified SMA. One such blend additionallycontained as an impact modifier a polyether ester segmented blockcopolymer containing approximately 50 percent soft (polyether) segmentsavailable commercially from du Pont under the trademark Hytrel®4056.Izod impact and heat deflection temperature (264 psi) data are given inTable VII.

                  TABLE VII                                                       ______________________________________                                                        Example                                                                       XXVIII XXIX                                                   ______________________________________                                        Blend Composition,                                                            wt %                                                                          PET               50       44                                                 Dylark® 338S  50       44                                                 Hytrel® 4056  --       12                                                 Properties                                                                    1/4" Notched Izod,                                                            ft.-lb./in.       0.5      1.1                                                1/8" Notched Izod,                                                            ft.-lb./in.       0.5      1.1                                                1/8" Unnotched Izod,                                                          ft.-lb./in.       11.4     26.0                                               HDT at 264 psi, °C.                                                                      99       89                                                 ______________________________________                                    

EXAMPLES XXX-XXXIII

Four PET/SMA blends were formed, each containing Hytrel®4056 as animpact modifier. The PET's used were Goodyear Vituf®5900, GoodyearCleartuf®7202A and Rohm & Haas X 5028-0.82 having intrinsic viscositiesof 0.59, 0.72 and 0.82, respectively. The rubber-modified SMA's wereDylark®338S and Dylark®350. The makeup of the blends and theirproperties are summarized in Table VIII.

                  TABLE VIII                                                      ______________________________________                                                  Example                                                                       XXX     XXXI    XXXII     XXXIII                                    ______________________________________                                        Blend Composition,                                                            wt %                                                                          PET (0.50 I.V.)                                                                           40        --      --      --                                      PET (0.72 I.V.)                                                                           --        40      --      --                                      PET (0.82 I.V.)                                                                           --        --      40      45                                      Dylark® 338S                                                                          40        40      40      --                                      Dylark® 350                                                                           --        --      --      45                                      Hytrel® 4056                                                                          20        20      20      10                                      Properties                                                                    Specific Gravity                                                                          1.206     1.200   1.201   1.191                                   Flexural Strength,                                                            10.sup.3 psi                                                                              10.1      10.1    10.6    9.8                                     Flexural Modulus,                                                             10.sup.3 psi                                                                              277       295     303     299                                     1/8" Notched Izod,                                                            ft.-lb./in. 1.2       1.1     1.2     1.3                                     1/8" Unnotched Izod,                                                          ft.-lb./in. 20.6      25.7    N.B.*   N.B.*                                   HDT, 264 psi, °C.                                                                  90        88      88      82                                      ______________________________________                                         *Did not break.                                                          

Various modifications of the invention are possible without departingfrom the scope of the invention as set forth in the claims.

We claim:
 1. A thermoplastic composition which comprises in intimateadmixture:(a) a polyethylene terephthalate, and (b) a rubber-modifiedgraft copolymer of a vinyl aromatic compound and an α,β-unsaturatedcyclic anhydride;said composition having a heat deflection temperatureof at least about 80° C. at 264 psi as measured by the ASTM procedure D648-72.
 2. A composition of claim 1 having a heat deflection temperatureof at least about 90° C. at 264 psi as measured by the ASTM procedure D648-72.
 3. A composition of claim 1 wherein (b) is a rubber-modifiedgraft copolymer of a styrene and maleic anhydride.
 4. A composition ofclaim 1 wherein (b) is a rubber-modified graft copolymer of styrene andmaleic anhydride.
 5. A composition of claim 1 wherein (b) contains about5-25 parts by weight of said cyclic anhydride, 40-85 parts by weight ofsaid vinyl aromatic compound and 5-30 parts by weight of the rubber. 6.A composition of claim 1 wherein the relative proportions of (a) and (b)fall within the range of from about 10 to about 90 weight percent of (a)with from about 90 to about 10 weight percent of (b), the total of (a)and (b) being equal to
 100. 7. A composition of claim 1 wherein therelative proportions of (a) and (b) fall within the range of from about20 to about 80 weight percent of (a) with from about 80 to about 20weight percent of (b), the total of (a) and (b) being equal to
 100. 8. Acomposition of claim 1 wherein said polyethylene terephthalate has anintrinsic viscosity of between about 0.5 and 1.2 as measured at 25° C.using a solvent consisting of 60 percent by weight phenol and 40 percentby weight of tetrachloroethane; wherein (b) contains about 5-25 parts byweight of said cyclic anhydride, 40-85 parts by weight of said vinylaromatic compound and 5-30 parts by weight of the rubber; and whereinsaid composition has a heat deflection temperature of at least about 90°C. at 264 psi as measured by the ASTM procedure D 648-72.
 9. Acomposition of claim 1 wherein said polyethylene terephthalate has anintrinsic viscosity of between about 0.5 and 1.2 as measured at 25° C.using a solvent consisting of 60 percent by weight phenol and 40 percentby weight of tetrachloroethane and wherein (b) consists essentially of arubber-modified graft copolymer of styrene and maleic anhydride.
 10. Acomposition of claim 9 wherein (b) contains about 5-25 parts by weightof maleic anhydride, 40-85 parts by weight of styrene and 5-30 parts byweight of the rubber.
 11. A composition of claim 10 wherein the relativeproportions of (a) and (b) fall within the range of from about 20 toabout 80 weight percent of (a) with from about 80 to about 20 weightpercent of (b), the total of (a) and (b) being equal to
 100. 12. Acomposition of claim 1 further including an impact modifier.
 13. Athermoplastic composition which comprises in intimate admixture:(a)polyethylene terephthalate having an intrinsic viscosity of betweenabout 0.4 and about 1.2 as measured at 25° C. using a solvent consistingof 60 percent by weight phenol and 40 percent by weighttetrachloroethane, and (b) a rubber-modified graft copolymer of styreneand maleic anhydride;said composition having a heat deflectiontemperature of at least about 80° C. at 264 psi as measured by the ASTMtest procedure D 648-72, the relative proportions of (a) and (b) fallingwithin the range of from about 30 to about 70 weight percent of (a) withfrom about 70 to about 30 weight percent of (b), the total of (a) and(b) being equal to
 100. 14. A composition of claim 13 further includingan impact modifier.
 15. A composition of claim 14 wherein the impactmodifier is a copolyetherester segmented block copolymer.
 16. Acomposition of claim 15 wherein said block copolymer containsapproximately 50 percent polyether segments.
 17. A composition of claim13 wherein said intrinsic viscosity of (a) is between about 0.5 and 0.9.